1. Field of the Invention
The present invention relates to a reinforced rubber hose, and in particular, to a reinforced hose such as, for example, a power steering hose, which is exposed to high-temperatures and which requires resistance to oil, such as mineral oil, or, similarly, for example, a reinforced hydraulic hose, used for conducting a vegetable oil, such as palm or coconut oil.
Although a power steering hose with a basic configuration of an inner tube 11, a reinforcing yarn layer 13 and an outer tube 15, as shown in FIG. 1, is the primary model described herein by way of example, the present invention is not limited to this configuration, but is also applicable, for example, to a reinforced rubber hose with a plurality of reinforcing yarn layers or with three or more rubber layers, while lacking an outer tube.
Abbreviations of rubber polymers used in this specification are defined below.
NBR . . . nitrile rubber PA1 hydro-NBR . . . hydrogenated nitrile rubber PA1 CSM . . . chlorosulfonic polyethylene PA1 CR . . . polychloroprene rubber PA1 EPDM . . . ethylene-propylene-diene rubber PA1 phr . . . parts per hundred parts of rubber, used for abbreviating a weight unit, otherwise known as a compounding unit, unless otherwise specified.
2. Description of the Related Art
A conventional hose comprises, for example, an inner tube, a reinforcing yarn layer contacting the outer surface of the inner tube, and, usually, an outer tube. The inner tube is formed of a vulcanized NBR rubber compound, the reinforcing yarn layer is formed of 6,6-nylon yarn (polyamide fiber), and the outer tube is formed of a vulcanized CSM rubber compound.
Recent demands for high speed performance of passenger cars have been met at the expense of generating high-temperatures in engine compartments, necessitating the creation of higher heat-resistant and oil-resistant reinforced power steering hoses.
In order to meet this need, hoses comprising an inner tube formed of a double-layer structure, having an inner-tube inside layer of a vulcanized hydro-NBR rubber compound and an inner-tube outside layer of a vulcanized rubber compound, such as NBR or similar compound characterized by superior heat resistance, are used in automobile engines. However, it is necessary to use hydro-NBR with hydrogenation of about 83% or more in order to ensure oil resistance and heat resistance. When such a hydro-NBR rubber compound is bonded with non-hydrogenated NBR by vulcanization with a sulfur agent, it is difficult to obtain sufficient bonding force, because the crosslinking points of sulfur vulcanization are reduced with increasing ratios of hydrogenation.
Japanese Patent Publication No. Hei. 6-86915 discloses a technique in which, usually, both the hydro-NBR compound forming the inner-tube inside layer and the NBR compound forming the inner-tube outside layer are made to be a peroxide vulcanization group, and, in addition, triazine or the like is added to the NBR compound in order to ensure adhesion to the reinforcing fiber layer. However, this technique teaches the blending of sulfur, triazine or other vulcanizing agents, in addition to organic peroxide, in the NBR rubber compound of the inner-tube outside layer. The result is a complex compound requiring strict control of the vulcanization temperature and time during its production. In addition, because both the rubber compound (NBR rubber compound) forming the inner-tube outside layer and the rubber compound (hydro-NBR rubber compound) forming the inner-tube inside layer are synthesized by vulcanization with organic peroxide, the rubbers require careful handling and strict control of the vulcanizing process. This is because the organic peroxide vulcanization agents have a higher reactivity than sulfur vulcanization agents, and therefore must be protected from exposure to heat, sunlight, and the like.